The present invention relates to a plant for transmitting electric power comprising a direct voltage network for High Voltage Direct Current (HVDC) and at least one alternating voltage network connected thereto through a first station, the station being adapted to transmit electric power between the direct voltage network and the alternating voltage network. At least one VSC converter which converts direct voltage into alternating voltage, and conversely converts direct voltage into direct voltage network, is provided along with apparatus for controlling the converter.
Such a plant has recently been known through the thesis "PWM and control of two and three level high power voltage source converters" by Anders Lindberg, Kungliga Tekniska Hogskolan, Stockholm, 1995, in which publication such a plant for transmitting electric power through a direct voltage network for High Voltage Direct Current (HVDC) is described. Before the issuance of the thesis, plants for transmitting electric power through a direct voltage network for High Voltage Direct Current have used line-commutated CSC (Current Source Converter) converters in stations for power transmission. IGBTs (Insulated Gate Bipolar Transistor=bipolar transistor having an insulated gate) for high voltage applications which may easily be turned on and turned off simultaneously, may be connected in series to form valves in VSC (Voltage Source Converter) converters for forced commutation. VSC converters are now an alternative for the transmission of electric power between a direct voltage network for High Voltage Direct Current and alternating voltage networks, and offer several important advantages with respect to the use of line-commutated CSCs in HVDC. Also, it is desired to find fields of use for this totally new type of plant, which is so far only theoretically described in the thesis mentioned above, which utilizes the particular advantages offered by such a plant with respect to other plants previously known for transmitting electric power.